The invention relates to a multi-function antenna system with a radar reflector having an extremely high broadband capability, which, with small dimensions, achieves high efficiency for communication applications and is suitable, in particular, for mobile applications.
Mobile communication takes up a considerable portion in the design of private, commercial and machine-to-machine applications. The bandwidth requirement has increased dramatically in recent years.
In order to cover the different areas of need, new technologies have been developed, frequency bands have been extended or released for mobile communication. At the same time, the demand and requirements for the secure transmission of events, sensor values or position and navigation data, which should be able to be used in real time as far as possible, are increasing.
The increase in the data rates requires a likewise considerable increase in the frequency ranges used for communication.
As a result of the distribution of the frequencies which was previously carried out with international coordination, the available resources are scarce and the frequency ranges which can be used are not directly side by side. The result of this is that a modern antenna system must cover a drastically wider bandwidth and should be able to be used for various communication principles.
The so-called 4G or LTE technology is becoming increasingly widespread.
The technical design of LTE requires the user terminal to have antennas which are suitable for the Multiple-Input, Multiple-Output MIMO technology in order to ensure a high data throughput.
At the same time, the maximum effective transmission power of the terminal is restricted by legislation, with the result that the regulatory requirements must not be exceeded here.
The so-called cell size of a mobile radio cell is designed for optimum customer coverage by the operators. The result of this is that the cell size is considerably smaller in conurbations than in areas with a low population density. However, small cell sizes also technically mean that the requirements imposed on the so-called link budget are considerably lower, inter alia as a result of the relatively short distance between the terminal and the mobile radio transmission mast. As a result, antennas which are not very efficient can also be used on the terminal without having to accept drastic losses in the data throughput.
This circumstance is different in rural regions or even in bodies of water near to the coast.
Extremely high requirements emerge when using mobile communication on watercraft and aircraft.
The number and type of communication applications are disproportionately greater than in land vehicles, for example, and are subject to considerably more stringent requirements on the antenna system to be used. Added to this is the usually large distance to the closest mobile radio transmission mast when using LTE, for example.
The antenna system must therefore be adapted to the conditions of use in a highly efficient way and in the best-possible manner. Losses, for example as a result of poor efficiency of the antenna system, should be imperatively avoided. Complicating factors for maritime applications are the very small available space for antennas, the already existing multiplicity of other antennas, the harsh environmental conditions, considerable mechanical stresses and the existence of a multiplicity of high-energy interference sources, for example radar systems in the immediate environment.
In shipping, a number of systems and methods are prescribed for the purpose of avoiding accidents, collisions and dangerous situations, for example the presence and use of radar systems.
Owing to the design, not all watercraft have the same radar cross section and, under certain circumstances, can scarcely be detected by the traffic radar of another ship. This is the case, for example, in small yachts, fishing boats and sailing boats. The use of additional radar reflectors is prescribed and is at least strongly recommended in some regions in order to increase the visibility, that is to say the radar cross section, of the watercraft.
Many antennas are designed solely for the use of one polarization and/or one frequency range. The combination of various frequency ranges and polarizations, while ensuring a high degree of separation/isolation inside an antenna arrangement, appears to be problematic according to the prior art.
The requirements for protecting nearby assemblies from overloading by other high-power services, for example radar applications, have previously been taken into account only inadequately or not at all in antennas.
Omnidirectional broadband antennas have been known for a long time both from mobile communication and from communication from fixed locations. Rothammel, Karl: “Antennenbuch (10. Auflage) [Antenna book (10th edition)” and Hall, Gerald L./ARLL: “The ARRL Antenna Book (13th edition)” describe so-called discone antennas which have an omnidirectional directional characteristic in the azimuth and have a broadband capability of up to 1:5. The structure, size and restriction to one polarization plane and the values in adjusting the antenna, the VSWR (Voltage Sounding Wave Ratio) and the direct exposure of the structure to the environment are disadvantageous, in particular.
DE 30 46 255 A1 describes a broadband antenna for the radio frequency band which has a transmission line coupled to a monopole antenna. The structure, size and restriction to one polarization plane are also disadvantageous here. The described VSWR of 1:2.5 is particularly critical. This value results in strong reflections and a deterioration in the power transmission and the adjustment of following assemblies. Furthermore, this is a conventional monopole antenna structure having a so-called ground plane. As a result, the emission of the energy is concentrated on higher elevation angles with increasing frequency.
The antenna described in DE 202 20 086 U1 is very well-suited as a directional antenna and accordingly does not have an omnidirectional characteristic of the antenna pattern in the azimuth. The restricted frequency range and the complicated control are disadvantageous, in particular. MIMO applications are possible to a limited extent.
EP 1 542 314 A1 describes a three-dimensional monopole design for so-called UWB (Ultra Wide Band) applications. The aim of UWB communication is, in particular, to allow very high data rates between devices which are spatially very close together, for example on a desk, when networking the devices. Like in DE 30 46 255 A1, the described arrangements constitute a monopole antenna above a ground plane, with the result that, although the arrangement is well-suited to installation on devices, for example laptops, the omnidirectional emission with a preferred direction at an elevation of 0° cannot be concentrated in broadband on account of the design and does not correspond to the subject matter of the described arrangement. The fact that none of the described embodiments allows a broadband capability of above 1:3.5 is likewise disadvantageous. Another disadvantage is that MIMO applications which are based on various polarizations, like in the case of LTE, do not appear to be possible.
The monopole antenna described in EP 2 683 030 A1 has a high broadband capability of 1. As becomes clear from FIG. 2A and FIG. 2B, the emission of the antenna cannot be omnidirectionally concentrated in the azimuthal plane in a disadvantageous manner. An additional disadvantage results from the preferred arrangement of the antenna inside the electronic circuit, as a result of which the efficiency and gain of the antenna are very highly limited.
DE 20 2013 102 314 U1 describes an antenna arrangement for MIMO applications which appears to be well-suited to LTE applications. The gain and polarization separation are suitable for use on terminals at a relatively large distance from the next LTE base station. The lack of omnidirectional emission and the restricted bandwidth of at most 1:3.3, based on the first frequency which can be used, are disadvantageous.
The mechanical design and the lack of opportunities to integrate other communication services and the susceptibility to mechanical vibrations are also disadvantageous.
The broadband antenna described in DE 102 35 222 A1 is in the form of a monopole with a dipole and disadvantageously has an omnidirectional antenna characteristic in the azimuthal plane with concentration of the radiation on an elevation plane of 0° only in part of the frequency range which can be used. Another disadvantage is the low efficiency in the lower frequency range. According to the exemplary embodiment, the antenna is not suitable for GSM, 3G or LTE communication services. The bandwidth which can be used with good efficiency is in a ratio of 1:6. The embodiment is associated with the disadvantage of a very small radar cross section. The type of mechanical design, which allows free oscillation of the antenna under the effect of vibrations, is likewise disadvantageous.
The above-mentioned arrangements are not suitable as a radar reflector or are suitable only to an extremely limited extent.
The previously known antenna designs cited on the basis of the examples have unsatisfactory properties with regard to their usability for a multi-function antenna of a very wide bandwidth, small dimensions with high efficiency and as a radar reflector.
So-called radar reflectors are used for the purpose of increasing the radar visibility of watercraft. The additional space requirement and the design are problematic. Passive radar reflectors are commercially available in different embodiments and vary in size between approximately 25 cm and 50 cm in diameter (ball design) and in height from 30 cm to 70 cm (tube design). The radar reflectors make it possible to increase the radar cross section in a technically good manner. Their unsuitability for other communication services is considerably disadvantageous.
Therefore, the invention is based on the object of providing a multi-functional compact antenna system of high broadband capability with a radar reflector, which is able to exhibit an omnidirectional antenna characteristic in the azimuthal plane, to maximize the radiation in the elevation plane close to elevation angles around 0° and which has high mechanical stability.